In the manufacturing of a luminescent screen for a CRT, three light emitting phosphors are deposited in triads across a useful screen area of an interior surface of a faceplate panel. Each triad is comprised of blue-, green- and red-emitting phosphor materials. It is known to provide an aluminum layer that overlies the phosphor materials to reflect light emitted by the phosphor materials outwardly through the viewing surface of the panel to the viewer. However, to maximize the light output, it is necessary to ensure that the aluminum layer is smooth and highly reflective. To accomplish this purpose, a layer of a filming material is disposed between the phosphor materials and the aluminum layer. The filming material provides a cushion that fills the interstitial spaces between the discrete phosphor particles and permits the aluminum layer to be applied as a smooth and uninterrupted surface. It is known in the art to test the integrity of the aluminized screen by measuring the thickness of the aluminum layer by means of an eddy current test. The eddy current method uses several pairs of inductor coils that are placed in proximity to the outside surface of the viewing faceplate of the panel, after aluminizing. One pair of coils is aimed at the center of the panel, and two other pairs are aimed at the 2 o'clock and 8 o'clock corners, respectively. One coil of each pair is excited by an rf power supply which induces a signal voltage in the second coil due to the very thin aluminum layer overlying the screen, on the inside surface of the panel. In the absence of aluminum, or in the case of very thin aluminum, the induced voltage signal is high, and the panel is rejected by comparing the voltage signal to a calibration standard. However, if the thickness of the aluminum layer is within the desired limits, the eddy current induced voltage in the second coil is lower and the aluminized screen is accepted. Unfortunately, the eddy current test is not foolproof and panels that have sufficient aluminum may be rejected because the aluminum layer is not smooth enough or continuous enough for eddy currents to form. Thus, a more reliable test that does not falsely reject good panels is desirable.
Subsequently, the faceplate panel is baked at a high temperature to remove the volatilizable constituents, including the layer of filming material. The aluminum layer contains small holes or pores through which the volatilizable constituents of the screen escape during screen bake without adversely affecting the reflectivity of the aluminum layer. The holes or pores in the aluminum layer can be utilized in a more reliable test which evaluates not only the quality of the aluminum layer, but also the effectiveness of the filming layer.